This invention relates to Multilayer Color Sensing Photodetectors and the method of fabricating such devices.
Photodetectors are used in a variety of applications such as digital cameras and video cameras. Photodetectors used in applications such as these may be one of a variety of devices including photodiodes, photoresistors, phototransistors and other photosensitive devices.
In both digital still cameras and digital video cameras, information about the color of the incident light is typically obtained through the use of filters that are present above the individual photodetectors. These filters allow light of only a specified color through to the underlying photodetector. If three colors of light are to be detected, three types of filters are required, and three photodetectors are often needed for each pixel.
The deposition of layers of polycrystalline semiconductor material separated by a dielectric layer is routine. In an article entitled Stacked Amorphous Silicon Color Sensors, by Dietmar Knipp et al., IEEE Transactions on Electronics Devices, Vol. 49, No. 1, January 2002, which is hereby incorporated by reference, there is described a multilayer photodetector structure used in the prior art. Three layers of semiconductor material are separated by two layers of intervening dielectric material. Other examples of prior art devices include: U.S. Pat. No. 5,949,073, dated Sep. 7, 1999, and describes, “a photodetector, a photo semiconductor element is covered by a cap with an incident window permitting incident light to penetrate through a translucent member. The photo semiconductor element detects a quantity of incident light penetrating through the translucent member of the incident window. The translucent member of the incident window is made of a material capable of suppressing the transmitting light quantity of incident light components having wavelengths less than 700 nm and larger than 900 nm. A photoelectric current output of the photosensitive semiconductor element is controlled by the incident light penetrating through the translucent member of the incident window. The photosensitive semiconductor element operates in multiple ways as a thermosensing sensor and a photosensing sensor.”
U.S. Pat. No. 6,177,710, dated Jan. 23, 2001, which is hereby incorporated by reference, describes, “a semiconductor waveguide type photodetector, a layered structure is formed on a semiconductor substrate, the layered structure formed by building a first semiconductor layer, a second semiconductor layer and a third semiconductor layer in due order, the first semiconductor layer being of one of p-type and n-type, the second semiconductor layer having lower bandgap energy than that of the first semiconductor layer, the third semiconductor layer having higher bandgap energy than that of the second semiconductor layer and having a conductive type opposite to that of the first semiconductor layer, and wherein at least the second semiconductor layer of the layered structure has a semiconductor waveguide having a mesa stripe structure, and at least a side surface and/or a light incidence end face of the second semiconductor layer is curved.”
U.S. Pat. No. 6,171,885, dated Jan. 9, 2001, which is hereby incorporated by reference, describes “a high efficiency color filter process for semiconductor array imaging devices, a microelectronic method is described for optimizing the fabrication of optical and semiconductor array structures for high efficiency color image formation in solid-state cameras. Disclosed is an ordered fabrication sequence in which microlens formation precedes color filter layer formation to enable increased image light collection efficiency, to encapsulate and protect the microlens elements from chemical and thermal processing damage, to minimize topographical under layer variations which would axially misalign or otherwise aberrate microlens elements formed on non-planar surfaces, and, to complete the most difficult steps early in the process to minimize rework and scrap. A CMOS, CID, of CCD optoelectronics configuration is formed by photolithographically patterning a planar array of photodiodes on a silicon or a III–V, II–VI or other compound semiconductor substrate. The photodiode array is provided with metal photoshields, passivated, planarized, and, a first convex microlens array of high curvature or other suitable lenses are formed thereon. A transparent encapsulating material is deposited to planarize the microlens layer and provide a spacer for the successive deposition of one or more color filter layers. The microlens array may be formed from positive photoresist and the spacer from negative resist, with close attention to matching the index of refraction at layer interfaces. A final surface layer comprising a color filter completes the solid-state color image-forming device”.